While a well developed complex of accessory glands is characteristic of the male reproductive tract of most mammals, including man, the role of these glands in fertility is unclear. There appear to be differences between species in the function of these glands. Seminal vesicle (SV) removal in boars and bulls has little or no effect on fertility, while in rodents, SV removal leads to infertility. Even among the rodents, the cause of infertility following SV removal may vary. In the rat, the vaginal plug appears to be necessary for fertility, but the plug is not necessary in the house mouse. In the house mouse, SV removal induced infertility is correlated with changes in uterine sperm motility and SV fluids fractionated by gel filtration have a direct effect on sperm motility in vitro. The purpose of this study is to compare the motility characteristics of mouse and rat sperm and to determine whether the SV fators which alter sperm motility in the mouse are species specific. Species specificity will be tested by incubating rat and mouse sperm in SV gel filtration fractions from each species and determining their effects on sperm motility. Dilution studies will also be performed to determine the relative sensitivity of the motility of sperm from each species to the influence of the SV factors. Sperm motility will be assessed by a videomicrographic method which provides objective, quantitative estimates of sperm swimming speed and the shape of the swimming path. The results of these studies should indicate whether motility controlling factors are likely to be a common feature of mammalian SV fluid and should help in the design of experiments to test for such factors in other species. In addition, if such factors are not species specific, isolation and identification of the factor from mouse SV would be informative. An understanding of naturally occurring factors that control sperm motility may lead to ideas for the development of new contaceptives.